Kin_Feb11.docx

Kinesiology 1080 – Feb. 11, 2013
Bulb of Brainstem
- It synapses onto the alpha motor neuron via monosynaptic connection (1 corticol
neuron synapses to 1 alpha motor neuron
Rostral & Caudal Parts of the Corticobulbar Tract
- Facial nucleus is divided into rostral (innervates forehead: upper facial musculature) and
caudal (innervates mouth: lower facial musculature) parts
 Rostral (Upper face)
 Innervates bilaterally
 It sends the projections to both sides of the body: left and right
 Caudal (Lower face – jaw area)
 Innervates contralaterally
 It sends the projections to the opposite sides of the body from the cortex
(left brain is controlling the right side of the body and vice versa)
- Tumor in cortex  It is an upper motor neuron injury which involves the corticobulbar
area
o This results in an asymmetrical innervation of the lower facial musculature
 A tumor in the right cortex will lead to a contralesional paralysis affecting the left
lower musculature. However, the upper face musculature is not affected by the
tumor because the rostral side sends signals bilaterally (both sides) and is able to
innervate the affected side
- Lower Motor Neuron Injury  Bell’s Palsy (Involves the axons of the alpha motor
neurons)
o Causes a complete paralysis of one side of the face
o When the lower motor neurons are impaired, no muscles in that area can be
innervated
o Both upper and lower facial musculature are affected
Corticospinal tract  It has two pathways: Ventral & Lateral
Ventral Corticospinal Tract  Simpler of the two corticospinal tract pathways  It originates from M1 (motor cortex),
SMA & PMA; but the vast majority is from M1
 It has a long axon that descends
(uncrossed) down the ventral columns of the
spinal cord, thus creating the ventral
corticospinal tract
 This is an ipsilateral connection
 Majority of these connections are
associated with innervating axial musculatures
 these are the muscles involved in large body
movements (large muscles)
 This tract also tends to make
connections with the propriospinal neurons 
they allow for communication of neural signals
between the segments of the spinal cord
 This is important because the
propriospinal neuron that is receiving the signal
can send its projections to numerous alpha motor neurons at different levels of the
spinal cord
 Then these alpha motor neurons are able to go on and innervate different back or trunk
muscles
 The ventral corticospinal tract allows for communication and coordination between
multiple muscle groups
 Example: Bending at the hips
 Multiple muscle groups required to support this movement 
Connection via propriospinal neurons innervates multiple alpha motor
neurons that might support the contraction of different types of
extrafusal muscle fibres
Lateral Corticospinal Tract  More sophisticated
 Originated from M1, SMA, PMA &
parietal cortex; majority of it originated
from M1
 This tract is not associated with the
ventral corticospinal tract in anyway
 75% of the fibres that make up the
lateral corticospinal tract cross over at the
level of the pyramids (pyramidal
decussation) Contralateral pathway
 It is very important** to know that
this pathway has primary monosynaptic